This invention relates to modified polyarylate resins which have good mechanical strength, resistance to color change, transparency, moldability and flame retardancy and also to compositions comprising the same.
Aromatic polyester copolymers prepared from aromatic dicarboxylic acids and bisphenols (hereinafter referred to simply as polyarylate resin or resins) and particularly, polyarylate resins prepared from terephthalic acid and/or isophthalic acid and 2,2-bis (4-hydroxyphenyl) propane (bisphenol A) have good mechanical strength, electric characteristics, flame retardancy, dimensional stability and transparency. The melt moldings of the copolymers have wide utility as various machine parts, films, fibers and the like.
The preparation of the polyarylate resin can be broadly classified into a melt polymerization process as disclosed in Japanese Patent Publication Nos. 38-15247, 38-26299 and 43-28119 and Ind. Eng. Chem., 51, 147 (1959), a solution polymerization process as disclosed in Japanese Patent Publication No. 37-5599, and an interfacial polymerization process as disclosed in Japanese Patent Publication Nos. 40-1959 and 38-3598.
Of these processes, the solution polymerization process has many drawbacks that expensive acid chlorides (derived from corresponding carboxylic acids by the use of reagents such as thionyl chloride) have to be used and solvents and acid acceptors are essential, requiring much labor for the recovery thereof and that washing and drying steps of the resultant polymer are necessary.
The interfacial polymerization process has, aside from the drawbacks involved in the solution polymerization process, the problem that additional labor is necessary for separation between aqueous and organic phases and the acid chloride may be hydrolyzed with water.
On the other hand, the melt polymerization process is free from those drawbacks involved in the solution polymerization process and the interfacial polymerization process, but has the following disadvantages.
Bisphenol A-based polyarylates comprised of bisphenol A, terephthalic acid and/or isophthalic acid do not exhibit satisfactory mechanical strength until the molecular weight reaches such a value that corresponds to an inherent viscosity of 0.40 dl/g or over. However, the viscosity of the product having such a molecular weight as mentioned above becomes as high as several thousands to several ten thousands poises at high as several thousands to several ten thousands poises at high temperatures, for example, of 350.degree. C. or higher, with a loss of properties as a fluid. This will make the agitation of the system difficult, thereby causing the organic acid or phenols produced by the ester interchange reaction not to be removed to a satisfactory extent. Polymers with a high degree of polymerization are difficult to obtain. In addition, the polymer is in contact with hot wall surfaces of a polymerization reactor over a long time and will undergo coloration or decomposition by local overheating.
Accordingly, it is substantially difficult to obtain, according to the melt polymerization process, bisphenol A-based polyarylates having good appearance and good mechanical strength. Industrially, they have been manufactured by the solution polymerization or interfacial polymerization process which is high in cost. However, if the above problems can be solved, the melt polymerization process is the most advantageous as an industrial process of preparing polyarylate resins.
In recent years, Japanese Laid-open Patent Application Nos. 48-88193 and 58-185615 proposed improved processes wherein thermoplastic polymers are added for preparing polyarylates by the melt polymerization process.
In the U.S. Pat. No(s). 3,684,766 and 4,075,173 have proposed processes wherein prepolymers are initially prepared according to the melt polymerization process and subjected to solid phase polymerization.
In the process, for example, disclosed in the Japanese Laid-open Patent Application 58-185615, the melting temperature and melt viscosity lower owing to the addition of thermoplastic polymer by which the difficulty in agitation at the time of polymerization and the problem accompanied by this can be solved. However, it takes a long time before the resultant polyarylate resin reaches a molecular weight sufficient to give satisfactory mechanical strength, during which the resin undergoes coloration. Accordingly, it is not possible to manufacture polyarylate resin having good mechanical strength and appearance.
The process disclosed in the U.S. Pat. No. 4,075,173 is a process wherein a prepolymer having a relatively small molecular weight is prepared in a low viscosity condition according to the melt polymerization process and is then heated in the form of the solid in an inert gas or under reduced pressure to cause the polymerization to proceed (solid phase polymerization process). This process needs an equipment for carrying out the solid polymerization, coupled with the problems of melt bonding of polymer and the non-uniformity in degree of polymerization. Thus, polyarylate resins of high quality cannot be obtained by this process.
Polyarylate resins which have a great demand in the fields of electric parts and automobile parts are also required to be in safety against fire. Various methods of imparting flame retardancy to polyarylate resins are known. In general, it has been widely used to incorporate in polyarylate resins a flame retardant such as an organic phosphorus compound or a halogen-containing compound with or without further addition of a flame retardant aid such as antimony trioxide. For the incorporation of the flame retardant in polyarylate resin, it is the most popular to subject polyarylate resins and flames retardants and/or aids thereof to melt kneading such as by extrusion (e.g. Japanese Laid-open Patent Application No. 60-155258, U.S. Pat. No. 4,259,458 and Japanese Laid-open Patent Application No. 53-94366).
However, since polyarylate resins have so high a melt viscosity that the melt kneading requires fairly high temperatures of, for example, 260.degree. C. or over, the flame retardant is liable to thermally decompose or the thermal decomposition of the resin ascribed to the flame retardant aid is apt to occur at the time of the melt kneading, thereby causing the resultant molding to be colored or to be lowered in strength. Additionally, there may arise a problem that the molding machine is corroded by generation of corrosive gases.
In order to solve the above problems, it is known to use a polymer-type flame retardant having a tetrabromobisphenol A skelton such as, for example, a halogenated polycarbonate. The polyarylate molding wherein such a polymer-type flame retardant is added singly or in combination with a flame retardant aid such as antimony trioxide is free from the problems, such as the coloration of the resin caused by the thermal decomposition of the flame retardant and the generation of corrosive gases during the molding operation, since the flame retardant has good thermal stability.
However, the flame retardant has poor miscibility with the resin, thus bringing about a lowering of transparency and a lowering of physical properties of the molding caused by failure in dispersion.
On the other hand, it is also known that for flame retardancy of thermoplastic polyesters, halogen-containing aromatic diols are copolymerized by melt polymerization at the stage of the preparation thereby imparting flame retardancy thereto (for example, Japanese Laid-open Patent Application No. 55-123619). However, with polyarylates for which the reaction temperature of the melt polymerization is generally high at 320.degree. C. or over, this method cannot solve the problems such as the coloration of the resin ascribed to the thermal decomposition of the halogen-containing aromatic diol and the corrosion of a polymerization apparatus produced by the generation of corrosive gases. In addition, because of the thermal decomposition, the degree of polymerization is difficult to increase. Accordingly, the resultant molding article suffers a substantial degree of coloration and has low mechanical strength.
For solving the above problem, a process is known wherein melt polymerization is carried out at temperatures at which the halogen-containing aromatic diol is not decomposed to prepare a prepolymer with a low degree of polymerization, after which it is polycondensed in a solid phase under a high degree of vacuum or in a stream of an inert gas thereby obtain a polyester which is substantially free of coloration with corrosive gases being generated only in small amounts and which has an appropriate degree of polymerization (Japanese Laid-open Patent Application No. 62-161826).
However, when this process is applied for polyarylate in order to obtain melt molding articles, a molding temperature of, for example, 320.degree. C. or over is necessary, eventually leading to a slight degree of thermal decomposition of the halogen-containing aromatic diol. A long time is necessary for the solid phase polymerization with attendant problems of a reduction of productivity and a necessity of an additional solid phase polymerization apparatus.
To be more important is that in either case of the addition of the flame retardant or the copolymerization of halogenated monomer, although the combustion time can be shortened, dripping of the melt during the combustion cannot be prevented. The improvement of the dripping property is very important from the standpoint of the spread of a fire.
In the fields of electric and electronic materials, for example, it is required to reduce the content of corrosive ingredients as small as possible from the standpoint of preventing corrosion of electrode. Accordingly, in these fields, use of known flame retardants and their aids containing corrosive components such as, for example, halides, antimony trioxide and the like is not possible. If these known flame retardants and aids therefor are used, limitation is placed on the application of such moldings.
As described above, an industrially appropriate process of preparing polyarylate resins by melt polymerization has not been established yet and thus, polyarylate resins having good mechanical strength, heat resistance, resistance to color change, transparency, moldability and flame retardancy have never been provided up to now.
It will be noted that the term "resistance to color change" is intended to mean unlikelihood to coloration during the preparation of polyarylate resins.
On the other hand, the polyarylate and polyamide are not miscible with each other and the composition obtained by melt kneading the mixture exhibits a phase separation structure wherein because the adhesion strength at the interface between the polyarylate phase and the polyamide phase is weak, the composition has a small impact strength and is brittle.
An object of the invention is to provide a polyarylate resin which is improved in moldability which is an inherent detriment to known polyarylate resins, which has good transparency, mechanical strength and impact strength without containing corrosive components and which are improved in flame retardancy and dripping properties.
Another object of the invention is to provide a thermoplastic resin composition of a polyarylate and a polyamide which is significantly improved in impact strength without a sacrifice of resistances to solvent and heat, moldability, high rigidity and thermal stability which are inherently possessed by those resin compositions.